The present invention relates to a refrigeration system. More particularly the invention relates to an extremely low temperature two-stage refrigeration system capable of utilizing refrigerant vapor and a slurry of solid sublimatable refrigerant particles in a liquid.
U.S. Pat. No. 5,715,702 to Strong et al. (hereinafter Strong) describes a refrigeration system using a slurry of solid refrigerant particles of a first substance and a liquid of a second substance. More particularly, Strong, discloses a system with a mixing tank for supplying a slurry of solid, sublimatable particles in a liquid to a sublimator. The sublimator returns sublimated particles and remainder slurry to a separator. The separator returns slurry to the mixing tank and sends the sublimated particles to a compressor and condenser. The condenser returns liquid refrigerant to the mixing tank for a new cooling cycle.
Referring to FIGS. 1 and 2, illustrating the prior art refrigeration system of Strong, the figure numbering convention will include a (xe2x80x2) to indicate that it is a feature of the prior art. The refrigeration system of Strong discloses a mixing tank 37xe2x80x2, separator 36xe2x80x2, an evaporator 3xe2x80x2, compressor 10xe2x80x2, a condenser 15xe2x80x2, and a receiver 16xe2x80x2, for use with a slurry of solid sublimatable particles in a liquid. The mixing tank 37xe2x80x2 has a first outlet 5xe2x80x2, second outlet 34xe2x80x2, a first inlet 31xe2x80x2, and a second inlet 17xe2x80x2. The evaporator 3xe2x80x2 has an inlet 6xe2x80x2 and an outlet 8xe2x80x2. A first conduit 4xe2x80x2 connects the first mixing tank outlet 5xe2x80x2 to the inlet of the evaporator 6xe2x80x2. The separator 36xe2x80x2 has a first inlet 9xe2x80x2, first outlet 31xe2x80x2, and second outlet 12xe2x80x2. A second conduit 7xe2x80x2 connects the evaporator outlet 8xe2x80x2 to the first separator inlet 9xe2x80x2. The separator 36xe2x80x2 discharges directly to the mixing tank 37xe2x80x2 by the shared opening separator first outlet 31xe2x80x2 and first inlet of the mixing tank 31xe2x80x2. A pipe 34xe2x80x2 and pressure regulator 35xe2x80x2 transfers vapor between the mixing tank 37xe2x80x2 and the separator 36xe2x80x2. The compressor 10xe2x80x2 has an inlet 11xe2x80x2 and an outlet 14xe2x80x2 and is connected to a condenser 15xe2x80x2 followed by the receiver 16xe2x80x2. A third conduit 13xe2x80x2 connects the second outlet of the separator 12xe2x80x2 to the compressor inlet 11xe2x80x2. A fourth conduit 19xe2x80x2 connects the receiver to the second inlet of the mixing tank 17xe2x80x2.
One of the problems with Strong, that the present invention seeks to solve, includes the potential plugging of the system due to the particles of refrigerant clogging or freezing shut conduits, valves, or inlets and outlets. Another problem is the energy requirements for this system are very high. The present invention has several improvements for addressing the potential system plugging, and also for significantly reduces the energy requirements of the system.
The present invention provides a refrigeration system for use with a refrigerant vapor and a slurry of solid sublimatable refrigerant particles in a liquid, where the refrigerant used in conjunction with the invention is preferably carbon dioxide (CO2) and the liquid is preferably d""limonene.
In a first embodiment of the present invention the intermediate slurry tank receives and stores CO2 vapor as well as a slurry of CO2 particles in the d""limonene liquid. The intermediate slurry tank is preferably maintained below the triple point of CO2. The intermediate slurry tank sends the slurry to the evaporator, the slurry being fed through a pump or by utilizing pressure and/or gravity from the intermediate slurry tank. A main slurry tank receives and stores the discharge from evaporator. The main slurry tank sends the remaining slurry back to the intermediate slurry tank, and sends the vapor CO2 to the compression system. The compression system also receives vapor CO2 from the intermediate slurry vessel, compresses the vapor from the main slurry tank and intermediate slurry tank and send it to the condenser. The condenser sends the condensate to the condenser receiving tank. The condenser receiving tank stores the liquid CO2 condensate and is maintained at a higher pressure than the intermediate slurry tank. The condenser receiving tank sends the liquid CO2 back to the intermediate slurry tank. The liquid CO2 is expanded either on its way to the intermediate slurry tank or in the tank itself. The expansion causes solid particles of CO2 to form from the liquid CO2. These solid CO2 particles are mixed into the slurry in intermediate slurry tank. The expansion of the liquid CO2 also results in vapor CO2 being produced.
In a further aspect of the present invention the conduit from the condenser receiving tank to the intermediate slurry tank may be modified to reduce refrigerant particle size as well as reducing the risk of plugging of the conduit or freezing of a valve in the conduit. The modifications may include: sloping the conduit, placing the point of refrigerant expansion close to the intermediate slurry tank, feeding gas into the system to add turbulence or heat, a special valve seat which forces the pressure drop to occur down stream of an expansion valve, or a direct injection system 200 to place the liquid refrigerant discharge directly into the intermediate slurry tank.
In a another aspect of the present invention a special slurry recirculation line is detailed. The recirculation line is designed to sweep the solid refrigerant particles off of a tank bottom to keep them suspended in the slurry.